The best way to melt someone's face off is undoubtedly the Plasma Cutter from the Dead Space series, a laser trident blaster that eviscerates all flesh in its path. Alas, such a thing is the whimsy of fictions.
Until now.
Fall to your knees, laser-less human: somebody done gone and made a working Plasma Cutter with deadly, working lasers. Cracking open the Plasma Cutter toy that shipped with the Dead Space 2 Collector's Edition, KipKay was able to mod it with real working lasers.
Unfortunately, commercially available lasers aren't all that deadly. However, you could use these lasers to a.) pop a balloon next to a person's face, startling them into falling out of a skyscraper window and b.) light a small pillow fire that could horribly scar someone's face if they didn't wake up during the process. Really, you are limited only by your imagination. And the Laser Safety Council.
KipKay teaches you how to make your own in this entertaining modding video, but don't come crying to me if you singe your precious, milky skin. Like most things awesome, this project is for adults only.